Nanoarchitectured manganese dioxide (MnO2)-based assemblies for biomedicine

The transition elements (groups IIIB to IIB)-based materials present advantageous morphological and physicochemical attributes due to the exceptionally variable valence states and highly stable metal ions. Among the first-row transition elements-based materials, manganese dioxide (MnO2) has garnered enormous interest from researchers due to the ease of fabricating diverse nanostructures in multiple dimensions (0-3D) with unique physicochemical, morphological, and optoelectronic characteristics. In addition to their excellent carrying ability as vectors, MnO2-based nanoarchitectures present several features of participating in the intracellular biochemical reactions and altering the internal tumor microenvironment. To preserve these exceptional features and improve biocompatibility, several MnO2-based architectures and nanocomposites have been fabricated. In this article, we provide a comprehensive view of various MnO2-based nanoplatforms in different forms, such as 0D (nanodots), 1D (nanowires and nanotubes), 2D (nanosheets), and 3D (nanoparticles and hollow spheres), as well as various innovative constructs (Janus-type and flower-shaped architectures). Initially, we provide insights on different engineering strategies, highlighting the pros and cons focusing on the reaction conditions. Further, we give a detailed exploration of these nanostructures and the offered properties that play crucial roles in their applicability. Then, we provide an emphasis on their applicability in diverse biomedical applications, such as conventional (drugs/photosensitizers/proteins/genes) and innovative therapeutic (chemodynamic, photodynamic, sonodynamic, and photothermal) modalities, bioimaging, biosensing, biocatalysis, cell capture/enrichment, as well as tissue regeneration. Finally, we summarize with interesting perspectives in addressing the challenges of translating these innovative platforms to clinics.